[ci] fix docsrs error for bdk crate

[notmandatory]

Description

Fixes #955

Notes to the reviewers

• Fixed by adding #![cfg_attr(docsrs, feature(doc_cfg))] to bdk crate lib.rs.
• Update nightly_docs workflow to use similar build command that docs.rs uses (and fails if above not done).
• For example docs artifact produced see: https://github.com/bitcoindevkit/bdk/actions/runs/5326442890

Changelog notice

none

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

[thunderbiscuit]

ACK 789cb99.

[LLFourn]

I've never heard of this feature before. Interested to see how this works. Unfortunately our new examples are in their own crates so this won't work there.

[notmandatory]

At least the bdk crate still has some code in it's own examples, and in the future it would be nice to put some simple examples in all the crates just to get the code added to the docs.

[notmandatory]

Nevermind, I removed the doc-scrape-examples feature, can add back later if we want it.

[LLFourn]

shouldn't you keep -Dwarnings.

[notmandatory]

The -Dwarnings isn't in the command that docs.rs uses so I left it off. I did confirm that with the new command string I added catches the feature(doc_cfg) issue when run locally or remotely. Also I can't see where in the docs that -Dwarnings is a flag that rustdoc cares about.
https://doc.rust-lang.org/cargo/commands/cargo-rustdoc.html

[notmandatory]

Correction: it looks like --cfg docsrs and -Dwarnings are both flags passed through to rustc. I'm pretty sure other jobs like clippy will fail first, but doesn't hurt to add it here also. I added it back as part of the build.rustdocflags and force pushed.

[notmandatory]

I rolled back all changes except the one I think really mattered which was adding #![cfg_attr(docsrs, feature(doc_cfg))] to bdk crate lib.rs.

If that's not enough to fix docs.rs I'll take another stab at it for the next alpha.

[notmandatory]

Ugh. Now with the -Dwarnings I seem to be getting a new error that I can't repro running the same command as on CI locally. Will keep looking into it tomorrow.

[notmandatory]

@LLFourn I simplified this down to just what should be needed to fix the original issue that was breaking the docs.rs rustdocs. Please approve if OK with you, this is the last thing before we can cut the alpha.1 release.

[LLFourn]

LGTM thanks @notmandatory